The first number is cold viscosity, second is hot viscosity. Once warm, 30 or 40, it doesn't make as much difference as the cold viscosity.

I have not had an issue running 15w40 amsoil all year in cold weather here was 4 out and turns over just fine. But the amsoil has a cold pour point in the -40 range or so.

I run amsoil diesel and marine blend. 15w 40. Seems to work pretty good. My oil pressure shoots up right away after starting. I hae been thinking about switching to Rotella Synthetic just so I dont have to keep ordering oil when I need a change. Where I live, we get 30 below often in the winter. I have actually started my truck in 47 below temps.

The reason I quoted your post is im curious what you run in your pickup?

I'm not a engineer in oil or engines,but a Kabota Diesel tractor and a cummins are two different engines.If the owners manual says to use one oil viscosity as per your climate cold or hot then stick to it.

Oil weight, or viscosity, refers to how thick or thin the oil is. The temperature requirements set for oil by the Society of Automotive Engineers (SAE) is 0 degrees F (low) and 210 degrees F (high).

Oils meeting the SAE's low temperature requirements have a "W" after the viscosity rating (example: 10W), and oils that meet the high ratings have no letter (example SAE 30). An oil is rated for viscosity by heating it to a specified temperature, and then allowing it to flow out of a specifically sized hole. Its viscosity rating is determined by the length of time it takes to flow out of the hole. If it flows quickly, it gets a low rating. If it flows slowly, it gets a high rating.

Engines need oil that is thin enough for cold starts, and thick enough when the engine is hot. Since oil gets thinner when heated, and thicker when cooled, most of us use what are called multi-grade, or multi-viscosity oils. These oils meet SAE specifications for the low temperature requirements of a light oil and the high temperature requirements of a heavy oil.

You will hear them referred to as multi-viscosity, all-season and all-weather oils. An example is a 10W-30 which is commonly found in stores. When choosing oil, always follow the manufacturer's recommendation.

Wondering how you can save money and protect your vehicle at the same time? Consider switching to synthetic oil and changing your oil at greater intervals.

Remember that the cummins has the cooling nozzles in the cylinders to cool the cylinder walls.

If the nozzles are intended to cool the liners, it's the first I have ever heard of it. I've seen and heard of piston cooling jets many times.

ive wondered why rotella didnt make a synthetic 15w40. i run the rotella 5w40 and have since i bought the truck in 04. and thats all i will put in it too. i worked for valvoline from 02-04 and to keep our certs for them we had to have so many hours of classes on oils and updates and what nots. i will never forget the last one i went to one of the dealers in atlanta asked, "ever diesel that comes in our shop wants rotella in their trucks, how do we convince them to buy a valvoline product?" one of the CEOs over sales replied "there is nothing we can say, the only problem with rotella is it doesnt say valvoline." that was all it took for me to know what i needed to about their products. if a CEO of a compeating company says its one of the best, what can you say to that.

i friggin run whatever we put in our tractors. its rotella somethin but iv read in some diesel books where they use that royal purple stuff. sounds like something more expensive than necessary to me though. :bat:

ya rotella synthetic is 19.95-25.00 depending on where you buy it at. royal purple is at the cheapest ive seen 34.95. works the same and cost 30-50 more a change depending on the size of your oil pan. ive tried royal purple before and didnt like it in engines. a friend ran it in his yoter and it made the valves chatter. went to ams oil in it and it stopped.

Like i said I run the 5w40 synthetic in the winter and rotella 15w40 in the summer. A guy that drives truck for my dad told me he's been running it in his pickups (7.3 powerstrokes) and he's the kinda guy whose truck looks brand new with 200,000 miles on it. So i've been using ever since. Only did one oil change with a different oil on my truck and that was before he talked to me

i run the 5w40 in mine year round. and thats all that will go in mine.